I disagree with you that the DE profits at th9 aren't as good as th10. I think the DE is much easier to get at th9, no infernos makes a huge difference. Sure can th10 bases offer more DE on a raid given the extra drill, yes, but that doesn't mean you are always getting all the DE a base has to offer every time.
I agree that th9 is a spike and it does require more effort to max your heroes at th9 then th10, but the ability to upgrade both heroes at the same time is much easier at th9 then at th10. For example once i hit th9 I upgraded my aq straight to 20 without stopping and once she hit 10 i was upgrading both my bk and aq to 20 at the same time. At th10 since the amount of DE needed to start a hero upgrade is much larger it becomes far more difficult to upgrade both at the same time, especially since miner nerf, but it's still possible if you are a hardcore farmer.
In my opinion th10 is not the place for the hero grind to be at. The gameplay changes drastically from th8 to th9 and then again from th9 to th10. I believe that it is in the best interest of most players to spend as much time at th9 as possible to learn how the more advanced strategies function and work on learning the end game tactics that are needed to be successful at th10 and 11.
The biggest point I can make is heroes are what tend to make the difference between 2 and 3 stars on a lot of planned out attacks. You state that the challenge of upgrading heroes at th9 drives people away, but those people were going to quit either way if that drives them away, because the game once you hit th9 is just a long grind period. th10 has a big elixir grind needed to start out, then you have to grind out the highest hero levels and grind out walls. I would argue that if the hero grind at th9 doesn't get them to quit then the other grinds at th10 will. There is nothing saying you have to max heroes before going to the next th.
Plus lets be honest hero upgrades are probably where SC makes a majority of its money. Lots of people will gem hero upgrades, especially aq, since they don't like raiding without her. As much as people like to complain about SC being greedy or changing the game so that it promotes more gem buying, as players this is something that we want whether you buy gems or not. If SC doesn't make money then there is no COC game for us to play, plain and simple. Just based on this alone is why I think the hero grind should be at th9 and not th10, might as well get people spending money as soon as possible.



